Water-soluble copolymer, polymeric flocculant, and method of dehydrating sludge

ABSTRACT

A novel water-soluble copolymer includes a polymer produced by polymerization of a water-soluble monomer and a polyalkyleneoxide oligomer having a specific ethylenically unsaturated group at one end thereof with. An aqueous solution of the polymer has a viscosity of 10,000 mPa·s or more (measured with a Brookfield viscometer, concentration: 20 weight percent). The water-soluble copolymer can be satisfactorily produced without causing problems such as gelation. When used in a sludge dewatering treatment, the copolymer provides flocs superior in flocculating strength, moisture content, and filtration rate. The water-soluble copolymer is useful as, for example, a retention aid, a paper strength agent, and a thickener. Also provided are a polymeric flocculant composed of the water-soluble copolymer and a method for dewatering treatment including the steps of adding the water-soluble copolymer to sludge and dewatering the mixture.

TECHNICAL FIELD

The present invention relates to a novel water-soluble copolymer usefulas a retention aid, a paper strength agent, a thickener, and inparticular, a polymeric flocculant, and to a manufacturing technology ofpolymers and a related technology of the above applications.

BACKGROUND ART

In general, water-soluble polymers, in particular, high-molecular weightwater-soluble polymers are used in various technical fields such aspolymeric flocculants, retention aids, paper strength agents, andthickeners.

Such water-soluble polymers include homopolymers prepared bypolymerizing an anionic monomer such as an acrylate or a methacrylate(hereinafter, acryl and methacryl are referred to as “(meth)acryl” incombination and acrylate and methacrylate are referred to as“(meth)acrylate” in combination), a cationic monomer such asdimethylaminoethyl(meth)acrylate quaternary salt, or a nonionic monomersuch as (meth)acrylamide and also include ionic polymers such ascopolymers of an anionic monomer and a nonionic monomer; copolymers of acationic monomer and a nonionic monomer; and copolymers of a cationicmonomer, an anionic monomer, and a nonionic monomer.

Various flocculants including a polymeric flocculant have been widelyused in order to flocculate and dewater sludge generated from municipalsewage and industrial wastewater. For example, in a method disclosed inJapanese Unexamined Patent Application Publication No. 58-51998,poly(iron sulfate) is used as an inorganic flocculant and a nonionic,anionic, or cationic polymeric flocculant is added alone to form flocsand dewater sludge. Japanese Unexamined Patent Application PublicationNo. 59-16599 discloses a method for dewatering sludge using an inorganicflocculant and an amphoteric polymeric flocculant having cationic andanionic properties. Furthermore, in a method disclosed in JapaneseUnexamined Patent Application Publication No. 63-158200, an inorganicflocculant is added to sludge and then the pH is controlled to 5 to 8.Subsequently, an amphoteric polymeric flocculant is added to the sludge.

In addition, various trials to improve polymers used as a polymericflocculant have been done. For example, Japanese Unexamined PatentApplication Publication No. 4-96913 discloses a flocculant composed of apolymer including a (meth)acrylate-terminated polyalkyleneoxide oligomerunit having an alkylene oxide skeleton being repeated 1 to 5 times, a(meth)acrylamide unit, and a cationic monomer unit. Japanese UnexaminedPatent Application Publication No. 11-156400 discloses a sludgedewatering agent composed of an amphoteric copolymer produced bycopolymerization of a cationic monomer, an anionic monomer, awater-soluble nonionic monomer, and a hydrophobic acrylic acidderivative having a solubility in water of 1 g or less, for example, analkyl(meth)acrylate having 8 or more carbon atoms, which are theessential components.

According to the polymers disclosed in the above patent documents, whichare used as a preferable flocculant or a sludge dewatering agent,however, problems reside in the polymerization steps of the monomers.For example, gelation readily occurs in the polymerization step. Inparticular, in the production of high-molecular weight polymers,gelation occurs entire in the reaction system. Unfortunately, when thepolymerization is performed with a view to avoiding gelation, only a lowmolecular weight polymer is produced, or a copolymer having a desiredcomposition cannot be produced. In the latter case, since thecopolymerization reactivity is significantly different in each monomer,a copolymer according to the initial ratio of each monomer is difficultto produce. Consequently, the desired improvement of the performancecannot be achieved. Even if the desired copolymer is produced, asufficient advantage cannot be achieved in some types of the targetsludge.

Furthermore, sludge generated from municipal sewage and industrialwastewater has been increasing because of changes in the recent livingenvironment. But the increase in consumption of flocculants and sludgedewatering machine must be suppressed. Therefore, flocculation anddewatering must be effectively performed with smaller amounts offlocculants or sludge dewatering agents. Flocculants and sludgedewatering agents having such a superior performance have been stronglydesired.

In view of the above situations, the present inventors studied for astable production of a polymer that is used as a polymeric flocculantand provides flocs having a superior balance in flocculating strength,filtration rate, and moisture content in sludge dewatering treatment. Asa result of the above study, the present inventors proposed a blockcopolymer prepared by polymerization of a water-soluble monomer underthe presence of a compound including a polyalkyleneoxide group having anazo group (Japanese Unexamined Patent Application Publication No.2002-97236).

Furthermore, the present inventors have continuously studied awater-soluble polymer that provides flocs excellent in flocculatingstrength, moisture content, and filtration rate. The water-solublepolymer has a superior property in flocculationability and also providesthe above superior dewatering effect of sludge for all types of sludge,in particular, even for sludge containing a large amount of excesssludge.

Consequently, the present inventors have found that a novelhigh-molecular weight water-soluble polymer including an essential unitcomposed of a polyalkyleneoxide oligomer having a specific ethylenicallyunsaturated group at one end thereof is satisfactorily produced withoutcausing problems such as gelation. When used in sludge dewateringtreatment, the water-soluble polymer provides flocs excellent inflocculating strength, moisture content, and filtration rate.Furthermore, the water-soluble polymer is useful as, for example, aretention aid, a paper strength agent, and a thickener.

Also, the present inventors have prepared the above novel water-solublepolymers having different cationic properties and have found the mixtureof them performs more efficiently the sludge dewatering treatment. Inother words, the present inventors have found that the dewateringtreatment, for example, in sludge containing a large amount of excesssludge, in which the ratio of the treatment of activated sludge inwastewater is higher than a known ratio in order to decrease the valueof chemical oxygen demand (COD) after the wastewater treatment, inparticular, in a sludge mixture including raw sludge and excess sludgecan be performed efficiently.

The present inventors have accomplished the present invention based onthis knowledge.

DISCLOSURE OF INVENTION

An invention described in claim 1 of the present invention provides awater-soluble copolymer comprising a polymer produced by polymerizing awater-soluble monomer with a polyalkyleneoxide oligomer having anethylenically unsaturated group represented by general formula (1) atone end thereof, wherein an aqueous solution of the polymer has aviscosity of 10,000 mPa·s or more (measured with a Brookfieldviscometer, concentration: 20 weight percent):R¹CH═C(R²)—X—  (1)[wherein each of R¹ and R² represents a hydrogen atom or an alkyl groupof 1 to 3 carbon atoms; X represents —R³O—, —O—, or —R⁴NHCOO—; each ofR³ and R⁴ represents an alkylene group of 1 to 4 carbon atoms, -Ph-, or-Ph-R⁵—; Ph represents a phenylene group that may have a substituent;and R⁵ represents an alkylene group of 1 to 4 carbon atoms].

An invention described in claim 2 of the present invention provides thewater-soluble copolymer according to claim 1, wherein the water-solublemonomer is comprising a cationic monomer or a mixture of a cationicmonomer and another monomer.

An invention described in claim 3 of the present invention provides thewater-soluble copolymer according to claim 1, wherein the water-solublemonomer is comprising a mixture of a cationic monomer and an anionicmonomer, or the mixture further including another monomer.

An invention described in claim 4 of the present invention provides thewater-soluble copolymer according to claim 1, wherein the number ofrepeating units of the alkylene oxide unit in the polyalkyleneoxideoligomer is 5 or more.

An invention described in claim 5 of the present invention provides thewater-soluble copolymer according to claim 4, wherein thepolyalkyleneoxide oligomer has an alkoxyl group of 1 to 8 carbon atomsat the other end thereof.

An invention described in claim 6 of the present invention provides thewater-soluble copolymer according to claim 1, wherein the polymer iscomprising a mixture including a polymer produced by polymerization of awater-soluble monomer containing 60 to 100 mole percent of a cationicmonomer and a polymer produced by polymerization of a water-solublemonomer containing 0 to 50 mole percent of a cationic monomer.

An invention described in claim 7 of the present invention provides thewater-soluble copolymer according to claim 1, wherein the polymer iscomprising a mixture including a polymer produced by polymerization of awater-soluble monomer containing 60 to 100 mole percent of a cationicmonomer and a polymer produced by polymerization of a water-solublemonomer containing 10 to 50 mole percent of a cationic monomer.

An invention described in claim 8 of the present invention provides apolymeric flocculant including a water-soluble copolymer according toany one of claims 1 to 7.

Furthermore, an invention described in claim 9 of the present inventionprovides a method for dewatering sludge including the steps of adding awater-soluble copolymer according to any one of claims 1 to 7 to sludge,and dewater the mixture.

BEST MODE FOR CARRYING OUT THE INVENTION

A water-soluble copolymer, a polymeric flocculant composed of thiswater-soluble copolymer, and a method for dewatering sludge using thewater-soluble copolymer of the present invention will now be describedin detail.

The water-soluble copolymer of the present invention is a copolymer of awater-soluble monomer and a polyalkyleneoxide oligomer having a specificethylenically unsaturated group at one end thereof. The copolymer has agraft skeleton in which the polyalkyleneoxide is bonded to the mainchain in a comb shape.

The ethylenically unsaturated group in the polalkyleneoxide oligomer isrepresented by general formula (1). Another ethylenically unsaturatedgroup such as a (meth)acryloyl group readily causes gelation in theproduction of the copolymer. Even if gelation does not occur, theresultant copolymer is not water-soluble.R¹CH═C(R²)—X—  (1)[wherein each of R¹ and R² represents a hydrogen atom or an alkyl groupof 1 to 3 carbon atoms; X represents —R³⁰—, —O—, or —R⁴NHCOO—; each ofR³ and R⁴ represents an alkylene group of 1 to 4 carbon atoms, -Ph-, or-Ph-R⁵—; Ph represents a phenylene group that may have a substituent;and R⁵ represents an alkylene group of 1 to 4 carbon atoms.]

The alkyl group of 1 to 3 carbon atoms in R¹ and R² is preferably amethyl group.

The symbol X represents —R³O—, —O—, or —R⁴NHCOO—. Another bond such asan ester bond readily causes gelation in the production of thecopolymer. Even if gelation does not occur, the resultant copolymer isnot water-soluble. The symbol X is preferably —R³O— or —O—.

Each of R³ and R⁴ represents an alkylene group of 1 to 4 carbon atoms,-Ph-, or -Ph-R⁵—; Ph represents a phenylene group that may have asubstituent, and R⁵ represents an alkylene group of 1 to 4 carbon atoms.

The alkylene group in R³ and R⁴ may be linear or branched. Examples ofthe phenylene group that may have a substituent include a p-phenylenegroup, an m-phenylene group, and the mixture thereof. The phenylenegroup is preferably a p-phenylene group. Examples of the substituent inthe phenylene group include an alkyl group and an alkyl ester group.

The alkylene group in R⁵ may be linear or branched. In particular, R³and R⁴ is preferably a methylene group or phenylene group.

Examples of the ethylenically unsaturated group represented by generalformula (1) include allyloxy, methallyloxy, allylethoxy, allylpropoxy,allylbutoxy, propenyloxy, and vinylbenzyloxy groups. In view of superiorreactivity and availability, allyloxy, methallyloxy, and propenyloxygroups are preferable.

Examples of the alkylene oxide that forms the main chain of thepolyalkyleneoxide oligomer include ethylene oxide, propylene oxide, andbutylene oxide. Specifically, examples of the polyalkyleneoxide oligomerinclude polyethyleneoxide oligomer, polypropyleneoxide oligomer, andpolybutyleneoxide oligomer.

The polyalkyleneoxide oligomer may include two or more of thesepolyalkyleneoxide oligomers as a block structure, for example,polyethyleneoxide/polypropyleneoxide block oligomer.

The number of repeating units of the alkylene oxide in thepolyalkyleneoxide is preferably 5 or more, more preferably, 5 to 80.When the number is less than 5, a flocculant or a dewatering agentprepared from the water-soluble copolymer does not have a sufficientdewatering performance. On the other hand, when the number exceeds 80,the unpolymerized material is increased and a flocculant or a dewateringagent prepared from the water-soluble copolymer does also not have asufficient dewatering performance.

The structure of the other end of the polyalkyleneoxide oligomer is notnecessarily limited. In order to achieve the object of the presentinvention, the other end of the polyalkyleneoxide oligomer is preferablyan alkoxy group of 1 to 8 carbon atoms such as methoxy, ethoxy, andbutoxy groups. In this case, the polymer can be stably produced withoutgelation.

In order to prepare these polyalkyleneoxide oligomers, a generalpolyalkyleneoxide oligomer is esterified, etherified, or urethanatedwith an alcohol or an isocyanate compound. Some of thesepolyalkyleneoxide oligomers are commercially available. Suchcommercially available oligomers may be used in the present invention.

Examples of the water-soluble monomer copolymerized with thepolyalkyleneoxide oligomer include a cationic monomer, an anionicmonomer, and a nonionic monomer that are industrially used. According tothe present invention, a cationic monomer or a mixture of a cationicmonomer and an anionic monomer is preferably used.

Any cationic monomer can be used without limitations as long as themonomer has radical polymerizability. Examples of the cationic monomerinclude tertiary salts such as hydrochlorides and sulfates ofdialkylaminoalkyl (meth)acrylates, e.g.,dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, anddiethylamino-2-hydroxypropyl(meth)acrylate; tertiary salts such ashydrochlorides and sulfates of dialkylaminoalkyl(meth)acrylamides, e.g.,dimethylaminopropyl(meth)acrylamide; quaternary salts such ashalogenated alkyl adducts, e.g., methyl chloride adducts and halogenatedaryl adducts, e.g., benzyl chloride adducts ofdialkylaminoalkyl(meth)acrylates; and quaternary salts such ashalogenated alkyl adducts, e.g., methyl chloride adducts and halogenatedaryl adducts, e.g., benzyl chloride adducts ofdialkylaminoalkyl(meth)acrylamides. In particular, tertiary salts orquaternary salts of dialkylaminoalkyl(meth)acrylamides are preferablyused.

Any anionic monomer can be used without limitations as long as themonomer has radical polymerizability. Examples of the anionic monomerinclude unsaturated carboxylic acids and salts thereof. Specifically,examples of the anionic monomer include acrylic acid, methacrylic acid,crotonic acid, itaconic acid, and maleic acid. Preferable monomers inthe present invention include acrylic acid and methacrylic acid.

Examples of the salts of the unsaturated carboxylic acids includeammonium salts and alkali metal salts such as sodium salts and potassiumsalts.

Examples of the nonionic monomer include (meth)acrylamide,dimethylacrylamide, diethylacrylamide, methyl acrylate, ethyl acrylate,butyl acrylate, hydroxyethyl acrylate, methoxyethyl acrylate,butoxyethyl acrylate, ethyl carbitol acrylate, acrylonitrile, and vinylacetate. In particular, (meth)acrylamide is preferably used.

Those cationic monomers, anionic monomers, and nonionic monomers may beused alone or in combination of two or more. As described above,essential components of the water-soluble monomer preferably include acationic monomer alone, or a cationic monomer and an anionic monomer.

When a cationic monomer is used, or when a cationic monomer and ananionic monomer are used, (meth)acrylamide is preferably used incombination as a nonionic monomer. This is preferable in thatcopolymerizability of the water-soluble monomers and the oligomer can beimproved and the characteristics of the resultant copolymer can becontrolled.

When (meth)acrylamide is used with a cationic monomer in combination,the ratio of (meth)acrylamide to the total of the water-soluble monomersis preferably 1 to 90 mole percent. When (meth)acrylamide is used with acationic monomer and an anionic monomer in combination, the ratio of(meth)acrylamide to the total of the water-soluble monomers ispreferably 5 to 80 mole percent.

Regarding the copolymerization ratio of the polyalkyleneoxide oligomerto the water-soluble monomers, the ratio of the polyalkyleneoxideoligomer to the total amount monomers is preferably 0.05 to 10 molepercent.

When the ratio is less than 0.05 mole percent, the improvement inflocculation due to copolymerization of the polyalkyleneoxide oligomeris not achieved. When the ratio exceeds 10 mole percent, a large amountof monomer that is not polymerized remains or the resultant copolymer isinsoluble in water.

When a cationic monomer and an anionic monomer are used in combinationas the water-soluble monomers, the ratio of the cationic monomer to thetotal amount of the water-soluble monomers is preferably 1 to 85 molepercent, more preferably, 5 to 50 mole percent. The ratio of the anionicmonomer to the total amount of the water-soluble monomers is preferably1 to 40 mole percent, more preferably, 1 to 30 mole percent.

In particular, according to the present invention, a preferablewater-soluble copolymer includes a mixture of a polymer prepared bycopolymerization of a water-soluble monomer including 60 to 100 molepercent of a cationic monomer and a polymer prepared by copolymerizationof a water-soluble monomer including 0 to 50 mole percent, morepreferably, 10 to 50 mole percent of a cationic monomer.

In order to produce a copolymer, a mixture of polyalkyleneoxide oligomerhaving an ethylenically unsaturated group, a water-soluble monomer, andanother polymerizable monomer that is used in combination according toneed are polymerized by a general method to produce a water-solublepolymer. In particular, the polymerization is preferably performed in anaqueous medium.

An aqueous solution polymerization will now be described as an exampleof such a polymerization in an aqueous medium. For example, an aqueoussolution containing 10 to 80 weight percent, preferably, 25 to 60 weightpercent of monomers is polymerized in the absence of oxygen using apolymerization initiator for 0.1 to 10 hours. The temperature at thepolymerization initiation is 0° C. to 35° C. and the polymerizationtemperature is 100° C. or less.

Examples of the polymerization initiator include persulfates such assodium persulfate and potassium persulfate; organic peroxides such asbenzoyl peroxide; azo compounds such as2,2′-azobis(amidinopropane)hydrochloride, azobiscyanovaleric acid,2,2′-azobisisobutyronitrile, and2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide]; and redoxcatalysts composed of a combination of, for example, hydrogen peroxideor sodium persulfate with sodium bisulfite or ferrous sulfate.

Polymerization may be performed with ultraviolet irradiation. Forexample, a photoinitiator composed of the ketals or acetophenones may beused for the polymerization.

The content of the polymerization initiator is determined according to,for example, the polymerization degree or viscosity of the desiredcopolymer. The content of the initiator is preferably 10 to 20,000 ppmbased on the total amount of all monomers and the polymerizationinitiator.

The molecular weight of the copolymer may be controlled by changing thetype and ratio of the monomers and the polymerization initiator used. Inaddition, a chain-transfer agent may be used to control the molecularweight of the copolymer by changing the type and ratio of thechain-transfer agent.

Examples of the chain-transfer agent include thiol compounds such asmercaptoethanol and mercaptopropionic acid; and reducing inorganic saltssuch as sodium sulfite, sodium hydrogen sulfite, and sodiumhypophosphite.

In the production of a high-molecular weight copolymer used as aflocculant, the content of the polymerization initiator is preferably 10to 2,000 ppm, whereas in the production of a copolymer used as apapermaking agent, the content of the polymerization initiator ispreferably 100 to 20,000 ppm.

According to a water-soluble copolymer described above, a polymer havinghigh cationic property and a polymer having low cationic property may beseparately prepared by polymerization, and may be then mixed to preparethe mixture. Any preparation method may be used. For example, the twopolymers may be mixed in advance, or may be mixed when the polymers areused. In addition, a plurality of polymers having a differentcopolymerization ratio of the cationic monomer unit may be preparedaccording as necessary.

According to the copolymer of the present invention, an aqueous solutioncontaining 20 weight percent of the copolymer has a viscosity of 10,000mPa·s or more, when measured with a Brookfield viscometer. Such a highviscosity is one of the reasons why this copolymer can be used forvarious applications. For example, the copolymer of the presentinvention is useful as a polymeric flocculant; papermaking chemicalagents used in the papermaking process such as a retention aid, a paperstrength agent, a pitch controller, and a sizing agent; a thickener usedfor, for example, a coating material; and a substrate for a plaster. Inparticular, the copolymer of the present invention is preferably usefulas a polymeric flocculant and a papermaking chemical agent.

The present invention is also applicable to a copolymer in which theweight-average molecular weight exceeds 1,000,000. An aqueous solutioncontaining 20 weight percent of such an ultrahigh-molecular weightcopolymer is a gel, and therefore, the viscosity cannot be measured.However, the copolymer can be used without a problem.

The copolymer produced in the present invention is, in particular,useful as a polymeric flocculant. The method for using the copolymer asa polymeric flocculent will now be described.

A copolymer having an average molecular weight in the order of a fewmillion to between ten and twenty million is preferably used as aflocculant. In particular, a 0.5% salted viscosity measured by a methoddescribed below is preferably 5 to 200 mPa·s, and a 0.1% insolubleresidue measured by a method described below after washing is preferably5 mL or less.

0.1% Insoluble Residue:

A copolymer is dissolved in purified water to prepare a 0.1 weightpercent solution (on the basis of a solid) (400 mL). The whole solutionis filtered through an 83-mesh sieve having a diameter of 20 cm. Theinsoluble residue on the sieve is recovered and the volume thereof ismeasured.

0.5% Salted Viscosity:

A copolymer is dissolved in an aqueous solution containing 4 weightpercent of sodium chloride to prepare a solution containing 0.5 weightpercent of the copolymer. The viscosity of the copolymer solution ismeasured with a Brookfield viscometer after 5 minutes at 25° C. and 60rpm.

The copolymer prepared by aqueous solution polymerization is usually agel. The copolymer is cut into chips by an existing method and is thendried with, for example, a belt dryer or a far-infrared dryer at about60° C. to about 100° C. The dried copolymer is milled with, for example,a roll mill to provide a powdery copolymer. Subsequently, the particlesize of the powdery copolymer is adjusted and, for example, an additiveis added to the copolymer. Thus, the resultant copolymer is used as apolymeric flocculant.

At the time of use, a polymeric flocculant of the present invention maybe mixed with an exisiting additive such as sodium hydrogensulfate,sodium sulfate, or a sulfamic acid as long as the additive does notcause any adverse effects on the dewatering treatment.

When added to various types of sludge, the polymeric flocculent of thepresent invention forms flocs having a superior balance in flocculatingstrength, filtration rate, and moisture content. There are no particularmethods for adding to the sludge and for forming flocs. Methods incurrent use can be satisfactorily applied. The sludge to which thepolymeric flocculant is applied is not particularly limited. Examples ofthe sludge include sludge generated from the treatment of domesticsewage, sludge generated from the treatment of wastewater from the foodindustry, sludge generated from the treatment of wastewater from thechemical industry, sludge generated from the treatment of piggerywastewater, and sludge generated from the pulp or paper manufacturingindustry.

Although the polymeric flocculant of the present invention can be usedalone, the polymeric flocculant may be used in combination with aninorganic flocculent or an organic cationic compound. Examples of theinorganic flocculant include aluminum sulfate, poly(aluminum chloride),ferric chloride, and poly(iron sulfate). Examples of the organiccationic compound include polymer-polyamines, polyamidines, and cationicsurfactants.

In particular, when the polymeric flocculant of the present invention isan amphoteric polymeric flocculant, the polymeric flocculant ispreferably added to sludge to which an inorganic flocculant is added.This dewatering method is more effective. In this case, after theaddition of the inorganic flocculant, the pH of the sludge is preferablyadjusted to 4 to 8, more preferably, 5 to 7.

The amount of the polymeric flocculant of the present invention to beadded to sludge is generally 0.1% to 3% on the basis of the dry solidcontent of the sludge, and is preferably 0.2% to 2% on the basis of thedry solid content of the sludge. When the amount of the polymericflocculant is less than 0.1%, the recovery of suspended substances fromthe sludge is insufficient. Even when the amount of the polymericflocculant exceeds 3%, no improvement in effect is observed.

When a mixture including a polymer having high cationic property and apolymer having low cationic property is used as the water-solublecopolymer, the ratio of both components is appropriately determinedaccording to, for example, the necessary amount of cation and the fibercontent in the sludge to which the copolymer is applied. The ratio,i.e., the polymer having high cationic property: the polymer having lowcationic property, is preferably 10:90 to 50:50 (by weight ratio). Whenthe ratio of the polymer having high cationic property is less than 10,dewatering treatment is insufficiently performed overall. On the otherhand, when the ratio of the polymer having high cationic propertyexceeds 90, the ability to form flocs becomes insufficient.

Although the details of this dewatering mechanism of sludge are notknown, the mechanism is supposed as follows: The polymer componenthaving high cationic property in the composition has a main role toneutralize electric charge in sludge. On the other hand, the polymercomponent having low cationic property has a main role to cross-link theformed flocs together. The use of these two kinds of polymers havingdifferent properties provides a superior effect in sludge dewateringtreatment, even in sludge containing a large amount of excess sludge.

The flocs formed can be dehydrated with a dewatering apparatus such as ascrew press dewatering machine, a belt press dewatering machine, afilter press dewatering machine, or a screw decanter to provide adewatered cake.

The flocculant of the present invention can also be applied to a methodfor dewatering with a flocculator having a filtration part.Specifically, an example of the method includes the following steps. Aninorganic flocculant is added to the sludge. The sludge is introducedinto a flocculator having a filtration part after the polymericflocculant is added to the sludge or together with the polymericflocculant. The filtrate is taken out from the filtration part andflocculation is simultaneously performed. The flocs are dewatered with adewatering machine.

The present invention will now be described in more detail withreference to Examples and Comparative Examples.

EXAMPLE 1

Allyloxy polyethyleneoxide monomethyl ether (the repeating number ofethylene oxide=9, trade name PKA-5010, molecular weight=1,500,manufactured by Nippon Oil & Fats Co., ltd. (i.e., NOF Corporation),hereinafter referred to as PKA-5010), an aqueous solution of quaternarymethyl chloride salt of dimethylaminoethyl acrylate (hereinafterreferred to as DAC), and an aqueous solution of acrylamide (hereinafterreferred to as AM) were prepared in a reactor made of stainless steel ina proportion of 1.0:85.0:14.0 by mole percent respectively. Distilledwater was added to the mixture such that the solution had a total weightof 1 kg and a total monomer concentration of 55 weight percent.

Subsequently, the temperature of the solution was controlled at 20° C.while nitrogen gas was bubbled into the solution for 60 minutes. Thus,an aqueous solution of a monomer mixture for polymerization wasprepared.

Subsequently, azobis(amidinopropane)hydrochloride (hereinafter referredto as V-50) and sodium hydrogensulfate were added to the solution inamounts of 1,000 ppm and 20 ppm, respectively, based on the weight ofall monomers. A 100 W black light irradiated the solution from above thereactor at an irradiation intensity of 6.0 mW/cm² for 60 minutes toperform polymerization, thereby producing a water-soluble copolymer inan aqueous gel form.

The water-soluble copolymer in an aqueous gel form was taken out fromthe reactor and was then cut into chips. The copolymer chips were driedat 80° C. for 5 hours and were then milled to prepare the powderywater-soluble copolymer. The copolymer had high-molecular weight. Sincean aqueous solution containing 20 weight percent of the copolymer was agel, the viscosity of the aqueous solution could not be measured.

This water-soluble copolymer was named polymeric flocculant P1, and the0.1% insoluble residue and the 0.5% salted viscosity of the polymericflocculant P1 were measured. Table 1 shows the results.

EXAMPLE 2 AND COMPARATIVE EXAMPLES 1 AND 2

Powdery water-soluble copolymers were produced as in Example 1, exceptthat the monomers, the initiator, etc. were changed to the conditionsshown in Table 1. The copolymers prepared had high-molecular weight.Since aqueous solutions containing 20 weight percent of the copolymerswere a gel, the viscosity of the aqueous solutions could not bemeasured.

The above water-soluble copolymers were named polymeric flocculant P2,R1, and R2, and the 0.1% insoluble residue and the 0.5% salted viscosityof the copolymers were measured. Table 1 shows the results.

In the table, PKA-5015 represents allyloxy poly (ethyleneglycol/propylene glycol)monobutyl ether [the ethylene glycol/propyleneglycol was a block copolymer having a molar ratio of 75:25], having amolecular weight of 1,600 (manufactured by NOF Corporation). In thetable, MEA represents methoxyethyl acrylate.

COMPARATIVE EXAMPLES 3 AND 4

Polymerization was performed as in Example 1, except that the monomers,the initiator, etc. were changed to the conditions shown in Table 1.However, the polymerization was not completed because of gelation.

In the table, AME400 represents acryloyloxy polyethyleneoxide monomethylether (number-average molecular weight 400, manufactured by NOFCorporation) and PME400 represents methacryloyloxy polyethyleneoxidemonomethyl ether (number-average molecular weight 400, manufactured byNOF Corporation). TABLE 1 COMPARATIVE EXAMPLES EXAMPLES 1 2 1 2 3 4POLYMERIC P1 P2 R1 R2 R3 R4 FLOCCU- LANT DAC 85.0 85.0 85.0 85.0 85.085.0 PKA1015 1.0 0.0 0.0 0.0 0.0 0.0 PKA5015 0.0 1.0 0.0 0.0 0.0 0.0 MEA0.0 0.0 1.0 0.0 0.0 0.0 AME400 0.0 0.0 0.0 0.0 1.0 0.0 PME400 0.0 0.00.0 0.0 0.0 1.0 AM 14.0 14.0 14.0 15.0 14.0 14.0 MONOMER 55.0 55.0 55.055.0 55.0 55.0 CONCEN- TRATION (wt %) POLYMER- 20 10 10 10 10 10 IZATIONINITIATION TEMP. (° C.) V-50 (ppm) 1000 1000 1000 1000 1000 1000NaHSO₃(ppm) 20 10 20 20 20 20 0.5% SALTED 19 24 21 20 — — VISCOSITY (mPa· s) 0.1% 0 0 0 0 INSOLUBLE INSOLUBLE RESIDUE (mL)

EXAMPLES 3 AND 4 AND COMPARATIVE EXAMPLES 5 AND 6

Sludge (200 mL) (SS: 10,000 mg/L, VSS: 8,100 mg/L) generated from theindustrial wastewater was prepared in a 500 mL beaker. Any polymericflocculants produced in Examples and Comparative Examples were added tothe sludge. Subsequently, the mixture was mixed with a stirrer for 90seconds to form sludge flocs. The particle diameters of the flocs weremeasured.

Then, the sludge floc dispersion was gravitationally filtered using an80-mesh net as a filter. The volume of the filtrate was measured after10 seconds. This value was shown as the filtration rate.

The resultant cake was compressively dewatered with a mini belt press(unit-area pressure: 0.5 kg/cm², three steps) to determine the moisturecontent. Table 2 shows these measurement results. TABLE 2 COMPARATIVEEXAMPLES EXAMPLES 3 4 5 6 POLYMERIC FLOCCULANT P1 P2 R1 R2 OPTIMALCONTENT (ppm) 150 150 150 150 FLOC DIAMETER (mm) 3˜4 4˜5 2˜4 2˜4FILTRATION RATE (mL/10 sec.) 122 130 110 109 MOISTURE CONTENT IN FLOC80.5 79.8 81.1 82.9 (wt %)

As is apparent from Examples 3 and 4, and Comparative Examples 5 and 6,polymeric flocculants in Examples have a superior filtration rate anddecreased moisture content in the floc, compared with the polymericflocculants in Comparative Examples.

When the moisture content in the floc is decreased by 2 weight percent,the amount of fuel oil used in the subsequent incineration process canbe reduced by 10 weight percent.

EXAMPLE 5

Polymerization was performed as in Example 1, except that allyloxypolyethyleneoxide monomethyl ether [manufactured by NOF Corporation,trade name PKA-5005, the repeating number of ethylene oxide=34,number-average molecular weight=1,500, hereinafter referred to asPKA-5005], DAC, and AM were used in a proportion of 0.3:95:4.7 by molepercent to produce a water-soluble copolymer in an aqueous gel form.Also, a powdery water-soluble copolymer was produced. This water-solublecopolymer was named A-1, and the 0.1% insoluble residue and the 0.5%salted viscosity of copolymer A-1 were measured. Table 3 shows theresults.

EXAMPLES 6 TO 8 AND COMPARATIVE EXAMPLE 7

Powdery water-soluble copolymers were produced as in Example 1, exceptthat the monomers, the initiator, etc. were changed to the conditionsshown in Table 3.

The 0.1% insoluble residue and the 0.5% salted viscosity of thewater-soluble copolymers were measured. Table 3 shows the results. TABLE3 EXAMPLE COMPARATIVE 5 6 7 8 EXAMPLES 7 COPOLYMER No. A-1 B-1 A-2 B-2C-1 MONOMER DAC 95.0 40.0 95.0 60.0 60.0 (mol %) AM 5.0 60.0 5.0 40.040.0 PKA-5005 0.3 0.3 PKA-5015 0.3 0.3 CONDITIONS MONOMER 55.0 55.0 55.055.0 55.0 CONCENTRATION (wt %) POLYMERIZATION 10 10 10 10 10 INITIATIONTEMP.(° C.) V-50 (ppm) 1000 1000 1000 1000 1000 NaHSO₃ (ppm) 20 20 20 2020 PHYSICAL 0.5% SALTED 20 20 20 20 20 PROPERTIES VISCOSITY (mPa · s)0.1% INSOLUBLE RESIDUE (mL) 0 0 0 0 0

EXAMPLE 9

Copolymers A-1 and B-1 were dissolved in water with a mixing ratio of35:65 (by weight ratio) to prepare a 0.2% aqueous solution. Thissolution was named flocculant 1.

EXAMPLE 10

Copolymers A-2 and B-2 were dissolved in water with a mixing ratio of57:43 (by weight ratio) to prepare a 0.2% aqueous solution. Thissolution was named flocculant 2.

EXAMPLES 11 AND 12

A sludge mixture generated from municipal sewage (pH=6.5, SS=23,000mg/L, VSS=18,000 mg/L) was used as a target sludge for treatment.Flocculant 1 or 2 was added to the sludge mixture. Optimal content, flocdiameter, filtration rate, and moisture content in the floc weremeasured as in Example 3. Table 4 shows the evaluation results.

EXAMPLE 13 AND COMPARATIVE EXAMPLE 8

Optimal content, floc diameter, filtration rate, and moisture content inthe floc were measured as in Example 11, except that a 0.2% aqueoussolution of copolymer B-2 (Example 13) or copolymer C-1 (ComparativeExample 8) was used as a flocculant. Table 4 shows the evaluationresults. TABLE 4 EXAMPLE COMPARATIVE 11 12 13 EXAMPLES 8 FLOCCULANTFLOCCU- FLOCCU- COPOLY- COPOLYMER LANT 1 LANT 2 MER B-2 C-1 OPTIMAL 160160 160 160 CONTENT OF FLOCCULANT (ppm) FLOC 5˜7 4˜5 2˜4 2˜4 DIAMETER(mm) FILTRATION 134 130 122 122 RATE (mL/10 sec.) MOISTURE 79.4 79.880.0 80.5 CONTENT IN FLOC (wt %)

Referring to the results shown in Table 4, flocculants composed of thewater-soluble copolymer of the present invention have a large flocdiameter, high initial filtration rate, and low moisture content.Accordingly, the flocculants of the present invention provide flocshaving superior performance.

INDUSTRIAL APPLICABILITY

The water-soluble copolymer of the present invention has high viscosityof an aqueous solution thereof, which is due to the structure, i.e., thegrafted structure having a branch of polyalkyleneoxide. Thewater-soluble copolymer of the present invention can be widely used forvarious applications such as a polymeric flocculant; papermakingchemical agents used in the papermaking process such as a retention aid,a paper strength agent, a pitch controlling agent, and a sizing agent; athickener used for, for example, a coating material; a builder used for,for example, a detergent; and a substrate for a plaster. Furthermore,the water-soluble copolymer of the present invention also shows superiorcharacteristics in the applications.

When water-soluble copolymers blended with two polymers having differentcationic properties are used as a polymeric flocculent, a superioreffect in sludge dewatering treatment is achieved in various types ofsludge, in particular, even in sludge containing a large amount ofexcess sludge.

1. A water-soluble copolymer comprising a polymer produced bypolymerizing a water-soluble monomer comprising a cationic monomer or amixture of a cationic monomer and another monomer with apolyalkyleneoxide oligomer having an ethylenically unsaturated grouprepresented by general formula (1) at one end thereof, wherein anaqueous solution of the polymer has a viscosity of 10,000 mPa·s or more(measured with a Brookfield viscometer, concentration: 20 weightpercent):R¹CH═C(R²)—X—  (1) [wherein each of R¹ and R² represents a hydrogen atomor an alkyl group of 1 to 3 carbon atoms; X represents —R³O—, —O—, or—R⁴NHCOO—; each of R³ and R⁴ represents an alkylene group of 1 to 4carbon atoms, -Ph-, or -Ph-R⁵—; Ph represents a phenylene group that mayhave a substituent; and R⁵ represents an alkylene group of 1 to 4 carbonatoms].
 2. (canceled)
 3. The water-soluble copolymer according to claim1, wherein the water-soluble monomer comprises a mixture of a cationicmonomer and an anionic monomer, or the mixture further comprisinganother monomer.
 4. The water-soluble copolymer according to claim 1,wherein the number of repeating units of the alkylene oxide unit in thepolyalkyleneoxide oligomer is 5 or more.
 5. The water-soluble copolymeraccording to claim 4, wherein the polyalkyleneoxide oligomer has analkoxyl group of 1 to 8 carbon atoms at the other end thereof.
 6. Thewater-soluble copolymer according to claim 1, wherein the polymercomprises a mixture comprising a polymer produced by polymerization of awater-soluble monomer containing 60 to 100 mole percent of a cationicmonomer and a polymer produced by polymerization of a water-solublemonomer containing 0 to 50 mole percent of a cationic monomer.
 7. Thewater-soluble copolymer according to claim 1, wherein the polymercomprises a mixture comprising a polymer produced by polymerization of awater-soluble monomer containing 60 to 100 mole percent of a cationicmonomer and a polymer produced by polymerization of a water-solublemonomer containing 10 to 50 mole percent of a cationic monomer.
 8. Apolymeric flocculant comprising a water-soluble copolymer according toclaim
 1. 9. A method for dewatering sludge comprising the steps ofadding a water-soluble copolymer according to claim 1 to sludge, anddewater the mixture.